The Physics and Chemistry of Artificial Intelligence — A Comparison with the Human Brain

The Human Brain from the Point of View of Physics and Chemistry

The human brain is a system that maintains a complex order within itself as long as energy continuously flows through it: it comes in with the blood, which carries oxygen and nutrients, and leaves into the surrounding world as heat. A candle flame and a whirlpool in a river work the same way: their form persists while the flow continues, and disappears when it stops. In physics, such systems are called non-equilibrium dissipative systems. The brain weighs about 1.4 kilograms and consists of roughly 10²⁶ atoms (a one followed by twenty-six zeros).

1. Foundation: long chains of carbon-based molecules (called polymers) that operate in a water environment.
2. Chemistry: about 97% of its mass comes from four elements — oxygen, carbon, hydrogen, and nitrogen. The rest is phosphorus, sodium, potassium, sulfur, chlorine, calcium, and tiny amounts of other substances, such as iron (which carries oxygen through the blood as part of hemoglobin), zinc, and copper.
3. Physical state: about three-quarters water. Substances are dissolved in it, and almost all chemistry happens there.
4. Engine and computer: proteins (which build, move, and process everything in the cell), the fatty membranes of cells, and DNA and RNA molecules that store and transmit instructions.
5. Computation (intelligence): from the point of view of physics, these are electrical and chemical signals. A nerve cell (neuron) at rest is charged: a difference in electrical charge of about 70 millivolts is maintained between its interior and the external environment (roughly 20 times less than in an AA battery). When a neuron receives a sufficient signal, a wave runs along its long process (the axon): for a moment the charge changes because charged particles of sodium and potassium (called ions) cross the cell membrane. This wave is called an action potential. Upon reaching the point of contact with a neighboring cell (a synapse), the signal causes the release of chemical messengers (neurotransmitters, such as dopamine, serotonin, and glutamate). They cross a tiny gap and act on the next cell.
6. Signal speed: from 0.5 m/s (a slow walk) to 120 m/s (about 430 km/h, faster than a Formula 1 car).
7. Energy and order (thermodynamics): the brain draws energy from the blood (glucose and oxygen, which come from food and air) and releases it to the surrounding world as heat. The order inside it (which physicists call low entropy) is maintained because disorder grows around it. An example from the cell: it continuously spends energy to maintain the charge difference between its interior and the external environment, and a significant share of the brain's energy goes into this. A living cell that has reached equilibrium with its environment is dead.
8. Origin: evolution by Darwin. Changes (mutations) arise randomly in hereditary material, and natural selection keeps those who are better adapted and produce offspring. The process took about 4 billion years.
9. Learning: the connections between nerve cells change: they strengthen, and new ones appear (cells grow new processes, called dendrites).
10. Connection with the world: the brain itself neither perceives nor moves anything: the sense organs and muscles are outside it and connected to it by nerves.
11. Conditions of existence: a constant supply of blood with oxygen and nutrients, a temperature of about 37 °C.

Servers on Which AI Runs, from the Point of View of Physics and Chemistry

Servers on which AI runs are devices that also maintain order through a flow of energy: electricity enters the microchips and leaves as heat. This order is needed for computation, that is, for multiplying enormous tables of numbers (mathematicians call them multidimensional tensors). One such server weighs on the order of 100 kilograms and consists of roughly 10²⁷ atoms, and a large AI runs on several servers. The silicon crystals of the computing accelerators in a single server contain only about 10²³ atoms; the rest is metal, plastic, and the cooling system.

1. Foundation: crystalline silicon (obtained from quartz sand, purified to extreme purity, and grown into crystals) and metal conductors inside microchips: solid devices with no moving parts. The microchips are placed in a metal housing with a cooling system.
2. Chemistry: the housing and cooling are mainly steel, aluminum, copper, and plastic. The microchips themselves consist mainly of silicon and oxygen (in the form of silicon dioxide SiO₂, the same substance as quartz and glass), as well as copper, aluminum, and gold, tantalum, tungsten, and other metals, including rare-earth elements.
3. Physical state: solid crystals operate inside the microchips, protected by a housing of plastic (a polymer) or ceramic.
4. Computation (intelligence): from the point of view of physics, this is the movement of electrons (the smallest charged particles) through billions of tiny switches, transistors. Each transistor either passes or does not pass current, like a switch. From their combinations, simple logical operations are assembled ("and," "or," "not"), and from these, any computation. Signals are transmitted by electromagnetic waves and pulses of light.
5. Signal speed: from 150 000 to 270 000 kilometers per second (from half to nine-tenths the speed of light).
6. Energy and order (thermodynamics): electricity enters the microchips, turns into computation, and almost entirely leaves as heat, which is why servers must be cooled. The order of computation is maintained because ordered electrical energy turns into the chaotic thermal motion of the crystal's atoms. Practically all consumed energy ultimately becomes heat.
7. Origin: they did not arise on their own but were designed and built by engineers over about 70 years.
8. Learning: the servers themselves do not learn: training happens earlier, on separate equipment, and its result is installed here.
9. Connection with the world: initially none; cameras, microphones, and speakers are connected to servers separately, and then robots, machines, and factories.
10. Conditions of existence: electricity, cooling, communication (data exchange channels), a dry, clean environment (moisture and dust harm microchips).

A Brief Comparison: The Brain and Servers Side by Side

The table is laid out in two columns so it is easy to read on a smartphone.

The Human Brain and AI Servers

The Human Brain	AI Servers
General principle: a non-equilibrium dissipative system: order is maintained as long as a flow of energy continues.	General principle: also a dissipative system: electricity comes in, heat goes out; order is needed for computation.
Mass and atoms: about 1.4 kg; roughly 1026 atoms.	Mass and atoms: about 100 kg per server; roughly 1027 atoms; in silicon accelerators, about 1023 atoms.
Foundation: carbon polymers in a water environment.	Foundation: crystalline silicon and metal conductors; solid microchips with no moving parts.
Chemistry: about 97% oxygen, carbon, hydrogen, and nitrogen; also phosphorus, sodium, potassium, sulfur, chlorine, calcium; traces of iron, zinc, and copper.	Chemistry: the housing is steel, aluminum, copper, and plastic; the microchips are silicon, oxygen as SiO2, copper, aluminum, gold, tantalum, tungsten, and rare-earth elements.
State: about three-quarters water; almost all chemistry happens in it.	State: solid crystals inside microchips, protected by plastic or ceramic.
Internal mechanism: proteins, fatty cell membranes, DNA, and RNA.	Internal mechanism: billions of transistors, from which logical operations "and," "or," "not" are assembled.
Computation: electrical and chemical signals; action potential, ions, neurotransmitters.	Computation: the movement of electrons through transistors; signals are transmitted by electromagnetic waves and pulses of light.
Signal speed: from 0.5 to 120 m/s (up to about 430 km/h).	Signal speed: from 150 000 to 270 000 km/s (about 0.5–0.9 the speed of light).
Energy and order: glucose and oxygen turn into heat; internal order is maintained by the growth of disorder outside.	Energy and order: electricity turns into computation and almost entirely leaves as heat; servers must be cooled.
Origin: Darwinian evolution, about 4 billion years.	Origin: designed and built by engineers over about 70 years.
Learning: connections between neurons change and strengthen; new processes can grow.	Learning: as a rule, they do not learn on site: the result of training is obtained in advance on other equipment and installed here.
Connection with the world: the sense organs and muscles are outside the brain and connected to it by nerves.	Connection with the world: initially none; cameras, microphones, speakers, robots, machines, and factories are connected separately.
Conditions of existence: a constant supply of blood, oxygen, nutrients, and a temperature of about 37 °C.	Conditions of existence: electricity, cooling, data exchange channels, and a dry, clean environment.

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